What is purpose and function of the Depth Map Assist Continuous AF (AF-D) mode?

The purpose and function of the Depth Map Assist Continuous AF (AF-D) mode.

AF-D allows the camera to track the focus of a subject on a wider area. In addition to the 19 AF areas used with the Continuous AF (AF-C) mode, AF-D also uses additional assist areas to help auto focus.

NOTE: AF-D is only compatible with select lenses. It is recommended you shoot images with AF-D if you have a compatible lens.